The present invention generally relates to an electric reversible motor control and, more particularly, to a motor control apparatus for use in association with an automobile air-conditioning system for controlling an electric reversible motor for bringing the automobile air-conditioning system into one of a plurality of air-conditioning modes.
There has long been well known an automobile air-conditioning system comprising an air intake duct and a plurality of distributor ducts branched off from one end of the air intake duct and opening into the interior of an automobile at various locations. The distributor ducts have respective air-mix shutter, vent shutter, and floor shutter installed therein for selectively closing and opening the associated distributor ducts so that not only can the direction and amount of flow of the conditioned air to be introduced into the automobile interior be controlled, but also a plurality of air-conditioning modes can be available one at a time by controlling the shutters according to a desired air-conditioning scheme, that is, by selecting a combination of the shutters to be controlled.
Examples of the above described automobile air-conditioning system are disclosed in the Japanese Utility Model Publications No. 47-852, published on Aug. 8, 1972, and No. 52-36446 published on Mar. 15, 1977. For controlling the motor operatively coupled to the air-mix shutter for selectively closing and opening a by-pass passage through a heat exchanger installed therein so that the air emerging from the air-conditioning system can be either cool or heated, respectively, the first-mentioned Japanese publication utilizes a control circuitry including a temperature sensor for sensing the temperature inside the automobile interior, a differential amplifier electrically connected to the motor, and a circuit for lowering the saturation level of an output from the differential amplifier.
On the other hand, in the second-mentioned Japanese publication, the various shutters are formed in a rotary hollow cylinder carrying the motor rigidly mounted thereon, the drive shaft of which motor extends into the hollow of the rotary cylinder and has a cylindrical fan mounted thereon. In other words, the motor used in the second-mentioned Japanese publication is solely used to drive the cylindrical fan, and the control of the shutters is effected by positioning the motor by the utilization of an electromagnetic device.
Except for the first-mentioned Japanese publication wherein the motor is controlled in response to change in temperature inside the automobile interior, the second-mentioned Japanese publication has failed to disclose a specific manner by which the motor is controlled, that is, a control circuit necessary to control the motor.